This application sets forth a method for optimizing valve timing events for a modern high speed, spark ignited internal combustion engine.
Modern internal combustion engines have typically provided good high speed performance characteristics by maximizing the engine's pumping capacity or "breathing". In other words, the engine has been made to perform well as a high speed pump. To achieve high speed pumping capacity, typical engine valving events are utilized such as: an early intake valve opening (in relation to top dead center or TDC) and a late exhaust valve closing (EVC). This results in a very large valve overlap during which both intake and exhaust valves are open simultaneously. It has long been standard practice that a large valve overlap is necessary for good engine power at high speeds.
Unfortunately, a large valve overlap also has the effect of greatly decreasing the engine ability to idle economically. In fact, to idle such an engine at a reasonably low speed, the standard practice is to to supply an overly rich fuel/air mixture to the engine and to use retarded ignition timing. This results in poor idle fuel economy.
The object of applying the subject method to engine valve events is to decrease valve overlap and hence improve engine idle fuel economy without substantially decreasing high speed performance. This is accomplished primarily by delaying the intake-valve opening (IVO) from traditional positions in relation to TDC. Resultantly, valve overlap is greatly decreased and idle performance and economy are enhanced.